1. Field of the Invention
This invention relates to methods and compositions for controlling a pest population. This invention is exemplified by a method for controlling growth of thrips, aphids, and spider mites on plants using a composition comprising a pest population controlling amount of a benzyl ester of an aromatic acid or aliphatic acid or a salicylate derivative.
2. Background of the Invention
Pests such as insects, arachnids, fungi, mites, and nematodes are detrimental to man. Pests include pathogenic organisms which infest mammals and plants; some of these pests can spread disease as disease vectors. The pathogenic organisms which infest plants and cause economic loss of plant crops include fungi, insects, arachnids, gastropods, and nematodes. The pathogenic organisms which infest animals include ticks, mites, fleas, and mosquitoes. Other pests include cockroaches, termites and ants.
Methods for controlling plant pathogens include spraying plants with fungicides on a 6-7 day schedule when environmental conditions favor disease development. These methods are typically used for controlling fungal infestations such as rust and powdery mildew. Typical fungicides used include heavy metals such as copper, mercury and arsenic, as well as organophosphorous and organic chlorine compounds. These compounds are often not satisfactory because of their potential for polluting the soils, their strong physiological effects on the plants, their residual toxicity in food crops, their high animal toxicity, and the potential hazards to workers using them.
Other methods of controlling pests such as insects and soil pests, such as nematodes and phylloxera, often involve the use of organophosphates, pyrethrum, pyrethroids (synthetic pyrethrum), mineral oil, oil, methoprene, and Baccillus thuringiensis israelensis crystal protein. Generally, these compounds are applied directly onto the pest population to control the organisms. Many of these compositions are toxic to large animals, including man, in addition to being toxic to insects or fungi. Further, many compositions that function as pesticides accumulate in the environment to levels considered to be unsafe. In addition, many of these compositions have been found to contaminate natural resources such as drinking water. Such problems have led the government to ban the use of many pesticides, including DDT, Chlorodane, Lindane, Aldrin, Heptachlor, Dieldrin, and Mirox. Other compositions, those still in use, present varying degrees of unwanted toxicity. Besides unwanted toxicity, presently-known pesticides have other problems. They tend to be complex and expensive to produce. It is often necessary to apply multiple pesticides to obtain satisfactory control of a variety of pests.
Biorational pesticides also are used in controlling pathogenic and pest organisms. A method of induction of systemic resistance to powdery mildew in cucumber by phosphates has been described (Reuvenl, et al. Biol. Agric. & Hort. (1993) 9:305-315). The phosphate salts serve the dual purpose of acting as a foliar fertilizer and as an agent for inducing resistance to pathogenic organisms. However, excessive use of phosphates produces agricultural runoffs that can cause water pollution. Methods for controlling powdery mildew and black spot on roses have been described (Plant Disease (1992) 76:247-251) which use sodium bicarbonate and light paraffinic petroleum oil. However, the bicarbonate salts are fungicidal only at pH 8.6 and are non-fungicidal at pH 6.0. The bicarbonate salts also can be phytotoxic as a function of environmental conditions at the time of treatment.
Also used for the control of powdery mildew in the field are anti-transpirants. Anti-transpirants are chemicals applied directly to a plant which reduce the rate of transpiration or water loss by the plant. Anti-transpirants form a film on a plant surface which acts as a barrier against invading pests. The anti-transpirant formulations are reported to have low mammalian toxicity, however, because the anti-transpirant controls pests through the formation of a protective barrier, it is useful only as a means of prevention rather than as a treatment of an already infected plant.
Therefore, it is of interest to identify and develop compositions and methods for controlling the growth of pathogenic and pest organisms which use formulations derived from natural products or are known to have lower environmental toxicity than the formulations currently in use, yet are effective in controlling insects and other pathogens without damaging a treated plant and/or plant part or a host tissue. It also is of interest to develop a new composition which is effective against more than one kind of pest so as to decrease the need for application of multiple pest control agents.
Relevant Literature
U.S. Pat. No. 3,983,214 discloses a fungicidal composition containing as an active ingredient, a C.sub.8-18 sucrose fatty-acid ester, and at least an adjuvant selected from the group consisting of a solid-carrier, a liquid-carrier, an emulsifying agent, a dispersing agent, and a surface-active agent.
Frances (J. Med. Entomol. (1994) 31(4):628-630) reports that E. hirsti (chiggar mite) larvae exposed to cloth treated with an ethanol solution of 5% benzyl benzoate caused 100% knockdown of test larvae in &lt;3 minutes.
Frances et al. (J. Med. Entomol. (1996) 33(2):232-235) disclose the toxicant effect of benzyl benzoate for scoring "knock-down" of a mite following exposure of chiggar larvae on white cotton fabric treated with benzyl benzoate in an ethanol formulation.
Brink-Lindroth, et al. (Acta Derm. Venereol (1984) 64:325) report killing human head lice eggs by applying benzyl benzoate (22.5 g) as a thin layer on the eggs, while Brown (Clin. Exp. Allergy (1994) 24:690) discloses a method of controlling the house dust mite with Acarosan.